Why is anyone using SQL server any longer? Even Microsoft heavily promotes PostgreSQL for big data: https://blogs.microsoft.com/bl...

Yes. The company 2ndQuadrant created something called Postgres BDR, and it is designed specifically for geographically diverse master-master replication.

Here are more details.

Did you ever try the Postgres built-in streaming replication? Kevin Grittner used to oversee the legal case databases for Wisconsin state courts. He has indicated several times that they've had better luck with Posgres replication than with SQL-Server replication.

I'll leave this here. It's an interesting series of videos that explain features of Postgres that SQL Server doesn't have. It also explains why many developers are moving from SQL Server to Postgres.

Pluralsight Tekpub Postgres videos

I know you were joking around, but in some (many?) cases, the document store mode of Postgres is faster than a comparable MongoDB installation.

Here is one such study.

Correction: MySQL used to be easier to use and administer.

Can you describe what makes MySQL easier to use and administer in present time (versus a few years ago)? I think nowadays they are on-par with each other for ease of use, especially if you're using Windows.

It has native "hot standby" replication- you can have one "write" database sever and many "read" servers, as the writes will replicate from the master to the slaves. As of version 9.5, a lot of the stuff will be baked in to the official Postgres to allow for multi-master replication. I reckon 9.6 will have it all the way there. For now, you can download Postgres BDR, which is a supported version of Postgres with multi-master replication.

It's not in BETA. It is a product that is fully supported (but still BSD licensed).